LADAR (Lasar detection and ranging) is simply radar transformed from measuring reflected radio frequency electromagnetic radiation, typically in the 1-25 cm wavelength range, to locate spatially removed objects, to a system that operates on laser radiation, typically in the 0.1 to 10.0 .mu.m range. The resulting combination of radar and optics provides a system with inherently enhanced accuracy in the measurement of range, velocity and angular displacement, and improved countermeasure resistance. Moreover, the high carrier frequency allows ladar systems to be made more compact in physical dimension, which is particularly attractive in aircraft, projectile, space and other volume-limited applications.
Disadvantageously, the penetrating ability of optical radiation is severely degraded by weather-related atmosphere disturbances. Consequently, the major developments in ladar technology have been directed at range-finding capabilities, particularly as fire control for mobile and air defense weapon systems and as a proximity fuzing device.
Until the recent advances in high-powered low-cost rugged continuous-wave (CW) semi-conductor lasers, most systems were based on pulsed solid state lasers that operated in a very low (.ltoreq.1.06 .mu.m) wavelength range, both hazardous to eyesight and ill-suited to the modulation techniques and processors required to achieve high range resolution (i.e., less than 30 cm) without resorting to non-linear super-resolution techniques and the attendant multiple target situation problems.
Moreover, self-clutter, a form of noise inherent to most FM equipment configurations, caused by irregularities and imperfections in mixer construction, produces a distorting signal frequently exceeding target signal by several orders of magnitude, consequently obscuring or confusing output target information. Comb filters have been developed to perform clutter subtraction but require a relatively substantial period of calibration or stabilization and, more importantly, are effective only with respect to time-varying or scanning applications and fail when applied to a stationary beam.